This invention relates to methods for recovering oil from a petroleum bearing earth formation by injecting fluids to flush oil from the pores of said earth formation and recover such oil at one or more recovery wells. More particularly, this invention relates to improved flooding processes for recovery of petroleum employing aqueous solutions of ammonium salts selected from the group consisting of ammonium sulfite, ammonium bisulfite and mixtures thereof as flooding medium, or as constituents thereof. According to the invention, aqueous solutions of said ammonium salts may be injected into a petroleum bearing earth formation as a bank of primary drive medium at ambient temperatures above the freezing point of said solution. Within the earth formation said aqueous solution may be heated by direct exchange with the earth formation, or by other means such as steam injection, to a temperature in the range of about 120.degree.-300.degree. F., or higher to provide an agent for driving oil from said earth formation to a recovery well.
For enhanced recovery of oil from petroleum bearing earth formations, it has become conventional practice to use a drive fluid under pressure to sweep oil remaining in said earth formation to a recovery well after primary production by gas drive, water drive or pumping has become uneconomical. Such sweep techniques may also be practiced early in the life of an oil field to maintain earth formation pressure. Normally for such enhanced recovery techniques one or more boreholes drilled into said earth formation are employed as injection wells and one or more boreholes, drilled into said earth formation at predetermined spacings from said injection wells, are employed as recovery wells. Sweep fluid, selected from oil miscible fluids, oil immiscible fluids, and combinations thereof, is injected into the injection wells and forms a bank of primary drive agent. The primary drive agent is then pressured through the earth formation, by injection of additional fluid, toward the recovery well or wells. Oil displaced from the earth formation by the sweep fluid is then produced from the recovery well or wells.
Oil recovery from subterranean formations is limited in enhanced recovery processes employing immiscible drive fluids, such as water and/or brines. Capillary forces and surface tension phenomena within rock pores of the subterranean formations prevent recovery of more than a fraction of the oil in place.
Use of a bank of primary drive agent miscible with the petroleum improves recovery of oil. Preferably in such processes oil miscible primary drive agent, such as liquefied hydrocarbon gases, carbon dioxide, etc. is injected into the oil-containing earth formation to form a bank of primary drive fluid. This primary drive fluid is pressured through the formation toward a recovery well by a backing drive fluid such as water, steam, additional gases, etc. The injection of primary drive agent is generally restricted in volume due to cost of liquids miscible with oil. The cost of enhanced recovery processes using oil miscible drive agents coupled with the relatively low value of additional oil recovered as a consequence serves to make such processes expensive, and not altogether successful, considering the amount of unrecovered oil remaining in subterranean formations after such recovery efforts.
Processes for enhanced recovery of oil from subterranean formations employing liquid sulfur dioxide, or aqueous solutions of sulfur dioxide as primary drive agent have been disclosed. For example see U.S. Pat. No. 3,353,597 and No. 3,326,289. Although such processes disclose improved recovery of oil, the disadvantages of handling a poisonous volatile, corrosive material such as sulfur dioxide are considerable.